This invention relates to an electrochemical process and more particularly to an electrochemical cell in which metal-oxides can be reduced to their corresponding metals. This process relies on the dissolution of the metal oxide into an electrolyte and subsequent decomposition or elective electrotransport. Thus, the process requires an electrolyte in which the metal-oxide is soluble.
There is an ongoing problem concerning the treatment of nuclear waste based on uranium oxide nuclear fuel. Currently, the oxide fuel is reduced electro-chemically or by chemically converting lithium to a metal in a molten salt. This head-end reduction step, with the elimination of oxygen, precedes an electrometallurgical process.
This invention relates to a method for the reduction of uranium oxide present in spent nuclear reactor fuels. More specifically, this invention relates to a single step process for the reduction of uranium oxide. Prior technology employed a two step process and two vessels using molten lithium chloride at 650° C. for the reduction of uranium oxide. In the first step, the oxide was chemically reduced to its metallic form by a reductant, lithium metal. Using this process, the uranium oxide to be converted is contained in a fuel basket generally constructed of a stainless steel mesh. Lithium oxide is the byproduct and is dissolved in the melt. In the second step, lithium oxide electrowinning, the dissolved lithium oxide is electrochemically decomposed to metallic lithium and oxygen gas. The recovered lithium and lithium chloride salt are then reused in the first step.
In a later development, a single step process was carried out using a single electrochemical cell. The negative electrode of this cell is the oxide basket itself, the metal oxides are reduced by a electrochemically generated reducing force. Some lithium metal may form simultaneously, but it is consumed immediately in a reaction with the oxide particles. Then, the Li2O, the byproduct of the cathode reaction diffuses from the cathode basket to the anode. At the anode the Li2O is electrochemically converted to oxygen gas and lithium metal, which is then reused.
In the subject invention, UO2 reacts with UCl4 which is dissolved in a molten LiCl salt bath. The LiCl salt bath may also contain KCl and UCl3 In reacting with the UCl4, the UO2 is converted to UOCl2 which is soluble in the molten LiCl—KCl—UCl4 salt. When a voltage is passed between an anode which may be carbon and is positioned in the UO2 containment vessel and a metallic cathode positioned in the salt bath containing the dissolved uranium chloride, the carbon anode is oxidized to form CO2 gas and UCl4 while at the cathode uranium metal is electroplated on the metallic cathode. During this process, new UCl4 is formed; thus, sustaining the reaction.
Thus, the objective of this invention is to provide a method of processing uranium oxide using a single step process.
Another objective is to employ this method with other transuranic oxides and rare earth metal oxides.
Additional advantages, objects and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.